html,body{
  width: 100%;
  height: 100%;
  border: 0;
  padding: 0;
  margin: 0;
  
}
.App{
  width: 100%;
  >.header{
    width: 100%;
    background-color: black;
    height: 40px;
  }
  .header div{
    float: left;
    background-color: aliceblue;
    height: 30px;
    padding: 0 10px;
    box-sizing: border-box;
    margin-top: 5px;
    line-height: 30px;
    border-radius: 3px;
    margin: 5px;

    a{
      color: black;
      text-decoration: none;

    }
  }
}